There are four different types of Kaposi's sarcoma (KS): Classic KS, endemic African KS, KS associated with immunosuppressive therapy, and epidemic/HIV-AIDS related KS.
KS is the most common AIDS-related neoplasia and contributes to morbidity and mortality in AIDS patients. The majority of cases of epidemic KS is seen in homosexual males with immunodeficiency of clinical significance. KS is currently afflicting approximately 20 000 AIDS patients annually in the United States (AIDS Weekly, Sep. 12, 1994). Up to 40 per cent of homosexual men with AIDS eventually develop KS.
The cause of KS is not yet known. Epidemiological studies indicate that a sexually transmissible agent is a factor of pathogenetic importance (Beral, V. et al: Kaposi's sarcoma among persons with AIDS: a sexually transmitted infection?, Lancet 335: 123-128, 1990, and Elford, J. et al: Kaposi's sarcoma as a sexually transmissible infection: an analysis of Australian AIDS surveillance data. AIDS 7: 1667-1671, 1993).
KS appears as reddish or purple lesions preferentially on the skin and mucous membranes of he gastrointestinal tract. About 50 per cent of cases exhibit lesions in the mouth. In advanced cases of KS lymph nodes and parenchymatous organs such as lungs and liver are frequently involved.
The KS lesions are often the only visible sign of AIDS and lead to severe psycho-social problems for the patient. During the course of KS the cutaneous lesions may become painful and secondary oedema from lymph node involvement may cause grotesque swelling of different parts of the body. Bleedings or obstruction of the gastrointestinal tract or the lungs occurs in advanced cases of KS.
Characteristic histopathological features of KS tumors include interweaving bands of "spindle cells" and vascular structures embedded in a network of collagen and reticular fibers. The presence of extravasated blood cells and hemosiderin is also characteristic. Whether or not KS is a true malignancy or merely a hyperplasia of certain tissues has been debated for quite some time. The isolation of KS cells from a patient exhibiting all the characteristics of a true malignancy has now been reported. At the same time it was claimed that a transmissible agent is not necessary for the pathogenesis of KS (Gallo, R. C. at The International Conference on AIDS in Yokohama, August, 1994).
Spindle cells characteristic of KS have been isolated from blood of HIV-infected patients with KS and, remarkedly, spindle cells have been isolated from a substantial proportion of HIV-infected homosexual men without any signs of KS (Gallo, R. C., ibid.). It might, therefore, be that KS can be diagnosed by the detection of markers in blood or secretions before visible lesions of KS appear in patients.
At present, there is no cure for KS or the immunodeficiency of HIV infection. The patients suffering from KS are currently offered chemotherapy, interferons, irradiation or different kinds of local treatment for palliation. Short remission and considerable side-effects limit the benefit of these therapeutic regimens. Continuous therapy is most often needed. Hair loss, nausea, vomiting, granulocytopenia with risk for bacterial infections, peripheral neuropathies and pulmonary problems are negative side-effects which significantly impair the quality of life of the patient.
Several studies have failed to show any significant anti-KS effect attributable to zidovudine, commonly known as AZT, which is an antiviral drug widely used against HIV-infection (Lane, HC et al.: Zidovudine in Patients with Human Immunodeficiency Virus Infection and Kaposi sarcoma, Ann Int Med 111, 41-50, 1989; de Wit et al.: Lack of activity of zidovudine in AIDS-associated Kaposi's sarcoma, AIDS 3: 847-850, 1989).
Foscarnet is an antiviral drug, which is presently being used in the treatment of patients infected with herpes simplex virus or cytomegalovirus. Foscarnet inhibits replication of herpesviruses in vitro including cytomegalovirus (CMV), herpes simplex virus types 1 and 2 (HSV-1, HSV-2), human herpesvirus 6 (HHV-6), Epstein-Barr virus (EBV), and varicella-zoster virus (VZV) as well as certain retroviruses, including the Human Immunodeficiency virus (HIV).
Foscarnet causes relatively few negative side-effects in patients as compared to cytostatics or interferons, the drugs presently being used in cases of KS.